Armature construction for double-insulated tool



y 1959 c. J. AMREIN, ETAL 3,447,011 I ARMATURE CONSTRUCTION FOR DOUBLE-INSULATED TOOL Filed on. :51, 1966 INVENTOR CARL J. AMREIN CHARLES V. CARMAN ATTORNEY United States Patent 3,447,011 ARMATURE CONSTRUCTION FOR DOUBLE- INSULATED TOOL Carl J. Amrein, Baltimore, and Charles V. Carmau, Fallston, Md., assignors to The Black and Decker Manufacturing Company, Towson, Md., a corporation of Maryland Filed Oct. 31, 1966, Ser. No. 590,626 Int. Cl. H02k 3/30 US. Cl. 310-235 18 Claims ABSTRACT OF THE DISCLOSURE A universal electric motor armature including armature windings and a commutator supported upon but insulated from an armature shaft. Bearings support the shaft at its ends and insulating means separates the commutator and the adjacent bearings.

This invention relates generally to electrical motor devices, and particularly to an improved, insulated motor armature construction for electrical tools and the like.

An important object of the present invention is to provide an improved, compact, insulated, electric motor armature construction adapted to meet high insulating standards.

A more particular important object of the present in vention is to provide an improved armature construction of the above type characterized in that it satisfies surface creepage distance requirements between the armature and both its shaft and shaft supports and accomplishes this with an overall axially compact construction.

Another important object of the present invention is to provide an improved armature construction of the above character, for which the insulating technique is easily adaptable for various sized motors and types of housings and armature support arrangements.

Further important objects of the present invention are to provide an improved armature construction of the above character which employs a minimum of separate parts and which is adapted for mass production forming and assembling techniques.

Additional objects of the present invention are to provide an improved commutator-and armature construction of the above character which is relatively inexpensive to manufacture, easy to assemble, durable in construction and reliable in use.

Other objects and advantages of the present invention will become more apparent from a consideration of the following detailed description taken in conjunction with the drawings in which:

FIGURE 1 is a view, partly in section, illustrating a universal electric motor armature embodying the present invention;

FIGURE 2 is an enlarged view of a portion of FIGURE 1 with parts removed, broken away and in section to more clearly illustrate the present invention; and

FIGURE 3 is a perspective view of the spring washer shown in FIGURES 1 and 2 and employed to resiliently support the aramature shaft in an axial direction.

Broadly described, the present invention includes an armature having armature windings, a commutator and an armature shaft, sleeve means insulating said shaft from said armature windings and commutator, said sleeve means having a first portion between and interconnecting said commutator and said shaft and having an annular groove in one radial face thereof increasing the creep length between said commutator and said shaft, and a second portion of said sleeve means between and inter- 3,447,011 Patented May 27, 1969 connecting said armature windings and said shaft and extending from the other side of said first portion opposite said one radial face.

Referring now more specifically to the drawings, a universal electric motor armature embodying the present invention is shown generally at 11 in FIGURE 1 and is seen to include an armature windings assembly 13 which is adapted to rotate within a conventional field subassembly (not shown). The armature 11 has an armature shaft 15 extending centrally therethrough and which is rotatably supported, fore and aft, by bearings 17, 19 respectively, carried by a motor frame 21. The bearings 17, 19 can, as shown, be spherical hearings, or alternatively, needle bearings can be employed. A motor cooling fan 23 is pressed on the armature shaft 15 to rotate conjointly therewith and the fan 23 is spaced from the bearing 19 by a washer 24. Typical uses for motors of this type are in power tools which include belt-type abrading, reciprocating and rotary tools. In the latter, the armature shaft 15 may extend through the hearing 19 and be formed with pinion teeth 26 at its outer end which drivingly engage a gear 28. The gear 28 may form a part of a transmission which interconnects the armature shaft 15 and a tool output spindle (not shown) so that upon energizing the motor 11, this spindle and the particular tool (not shown) associated therewith are rotatably driven.

A commutator, forming a part of the armature 11, is seen to include a bar segment 25 provided with terminal tangs 27 adapted to be connected with the armature windings in the usual manner. The commutator bar segment 25 is disposed in spaced, surrounding relation to the armature shaft 15 and the bar segment together with the armature windings assembly 13 are insulated from the armature shaft 15 by a novel insulating sleeve means generally illustrated at 29.

As seen best in FIGURE 2, the sleeve means 29 comprises a first portion 31 constructed of a mass of rigid, preferably moldable insulating material selected from those materials having high mechanical strength, electrical insulating and heat transfer properties. For example, asbestos and glass filled phenolics have been found to be particularly useful here. The material is molded in place within the commutator bar segment 25 in interlocking relation with preferably radially inwardly extending locking tangs 33 thereon. The sleeve portion 31 substantially fills the cavity between the commutator bar segment 25 and the armature shaft 15 and may have a bushing 35. preferably constructed of brass or steel, positioned therein and adapted to be press fitted on the shaft 15. Conveniently, the bushing 35 may be located within the bar segment 25 and insulating material thereafter molded in place to form the integrated commutator assembly shown in FIGURE 2. This assembly is then pressed on the armature shaft. On the other hand, if no bushing 35 is employed, the armature shaft 15 may be staked or otherwise has its surface irregularly formed to interlockingly engage the molded sleeve portion so that the commutator bar segment 25 rotates with and is supported upon the shaft 15.

As shown in FIGURE 2, the bushing 35, if one is employed. otherwise the molded material forming the sleeve portion 31, does not extend the full axial length of the sleeve portion 31 so that when the latter is in place on the armature shaft 15, a recess 37 is formed between the sleeve portion 31 and the shaft 15. According to one feature of the present invention, the sleeve means 29, includes a second portion 39 also constructed of a rigid, insulating material carried on the armature shaft 15 and having one end thereof received in the recess 37. The sleeve portion 39 also preferably is constructed of a material having high mohanical strength, electrical insulating and heat transfer properties and if a moldable material such as that employed to form the sleeve portion 31 is used to form the sleeve portion 39, the latter may be molded directly on the armature shaft 15 and within the armature windings assembly 13. Alternatively, the sleeve portion 39 can be molded or otherwise formed separately, machined and suitably mounted on the armature shaft 15 and within the armature windings assembly 13. In the latter methods, the same or a similar moldable material such as that described above for the sleeve portion 31 can be used or other suitable materials, for example, ceramic materials possessing the desired physical properties may be selected.

It is also within the scope of the invention to form the sleeve portions 31,. 39 integrally. In any event, the sleeve portion 39 is secured to both the shaft 15 and the windings assembly 13 by staking, grooving, keying or other suitable means and extends fully through and insulates the assembly 13 from the shaft 15 and preferably terminates just short of a mounting flange 41 on the fan 23.

The positioning of the sleeve portion 39 within the recess 37 prevents the end turns (not shown) connecting the terminal tangs 27 and the armature windings from contacting the armature shaft 15 during use. Furthermore, the total axial and radial length of the engaged surfaces of the sleeve portion 39 and the sleeve portion 31 within the recess 37 together with the radial length of the sleeve portion 31 outwardly of the sleeve portion 39 is selected to meet the necessary insulation surface creep length specifications, for example, the conventional Underwriters Laboratories double insulation specifications. Thus, by providing the relatively long axial recess 37 and positioning the end of the sleeve portion 39 therein, the necessary insulating requirements are met with a minimal overall axial length of the device. It will be appreciated that if desired, the engaged axial length between the sleeve portions 31, 39 at the recess 37 can be varied to handle even more stringent insulating requirements if necessary without affecting the overall axial dimension of the device. Also, the armature components thus far described are easily assembled and require no special fasteners or skill and are highly adapted for automatic assembly.

The rearward or left-hand end of the insulating sleeve portion 31 extends axially beyond the commutator bar segment 25 and beyond the shaft mounting bushing 35. According to an important aspect of the present invention, the rearward, radial face of the sleeve portion 31 is formed with an annular groove or trepan 43. The length of each axial face of the groove 43 adds to the surface creep length of the insulating sleeve portion 31 between the commutator bar segment 25 and the shaft 15 so that here again the axial length of the sleeve portion 31 and therefore the overall axial dimension of the device is minimized while satisfying the necessary insulating standards. Furthermore, if desired, this creep length can be increased still further by forming a conical taper 45 on the sleeve portion 31 adjacent the armature shaft 15. Of course, the length of the taper 45 and the depth of the groove or trepan 43 can be varied as might be deemed necessary in particular installations.

The armature shaft 15 is resiliently, axially supported relative to the bearing '19 and the frame 21 by a metallic, dish-shaped spring washer 47. A fiber washer 49 is positioned on the shaft '15 between the spring washer 47 and the bearing 19 and has a radial dimension smaller than the radial dimension of the spring washer 47 so as not to be cut by the edges thereof during shaft rotation. A stepped, insulating spacer 51, constructed of any rigid, high electrical insulating and heat transferable material is positioned on the shaft 15 between the spring washer 47 and the sleeve portion 31. As shown in FIGURE 2, the spring washer 47, by reason of its configuration, necessarily engages the fiber Washer 49 and the insulating spacer 51 at different radial locations. Thus, to insure that these parts rotate together and do not wear excessively, the

washers 47, 49 and the spacer 51 are loosely disposed on the armature shaft 15. Thus, the washers 47, 49 and the spacer 51 will by friction rotate oonjointly irrespective of the radius of their contact surfaces.

The spacer 51, being constructed from insulating material, functions together with the sleeve portion 31 to insulate the commutator bar segment 25 from the metallic spring washer 47. As shown in FIGURES l and 2, the spacer 51 has a radially outwardly extending step or flange 53 at the end thereof remote from the sleeve portion 31. The spacer 51 at the area of engagement with the sleeve portion 31 has a radial dimension equal to or less than the smallest radial dimension of the groove 43.

i The creep length between the commutator bar segment 25 and the washer 47 is measured by the sum of the exposed, axial length of the sleeve portion 31, the radial dimension of the sleeve portion 31 outwardly of the spacer 51, and the axial length of the spacer 51 together with twice the axial length of the groove or trepan 43 and the radial dimension of the spacer flange 53. Thus, the groove 43 and the flange 53 measurably increase this creep length without contributing to the overall axial length of the device. In addition, the spacer flange 53 is spaced axially from the sleeve portion 31, a dimension suflicient to prevent arcing across the sleeve portion 31 and the flange 53.

The insulating sleeve construction 29 of the present invention, which includes the formed sleeve portions 31,

39, and the stepped spacer 51 function as described to insulate the commutator bar segment 25 and the armature windings assembly 13 from the armature shaft 15 and the spring washer 47 and are formed to the configuration and relative dimensions as described above to satisfy the Underwriters Laboratories double insulation standards. In addition, the groove 43 and the recess 37 in the sleeve portion 31 together with the flange 53 on the spacer 51 and the sleeve portion 39 associated with the groove 43 and recess 37, respectively, provide the necessary surface creep dimensions and serve to materially reduce the overall axial dimensions of the device.

Furthermore, construction of the present invention is relatively inexpensive to manufacture and assemble. Thus, the sleeve portion 39 may be molded directly on the armature shaft 15 within the assembly 13 or separately as described above. The sleeve portion 31 is preferably molded directly within the commutator bar segment 25 with the bushing 35 in place and this assembly is pressed on the shaft 15 beyond and partially receiving the end of the sleeve portion 39. Thereafter, the molded spacer 51, the spring washer 47, the fiber washer 49 and the bearing 19 are slipped in place on one end of the shaft 15 and the fan 23, the washer 24 and the bearing mounted on the other end thereof after which the assembly is mounted in place in the frame 21.

By the foregoing, there has been disclosed an improved, insulated, armature construction calculated to fulfill the inventive objects set forth above, and while a preferred form of the present invention has been illustrated and described in detail, various additions, substitutions, modifications and omissions may be made thereto without departing from the spirit of the invention as encompassed by the appended claims.

We claim:

1. In an electric motor, an armature having armature windings, a commutator, and an armature shaft, sleeve means insulating said shaft from said armature windings and commutator, said sleeve means having a first portion between and interconnecting said commutator and said shaft, said first sleeve portion having an annular groove in one radial face thereof increasing the creep length between said commutator and said shaft, and a second portion of said sleeve means between and interconnecting said armature windings and said shaft and extending from the other side of said first portion opposite said one radial face.

2. An insulating construction for electric motors comprising an armature shaft, an associated armature windings assembly and commutator disposed for rotation with said shaft, sleeve means including a first and second portion within and interconnecting said commutator and said armature windings assembly, respectively, with said shaft but insulating the same therefrom, said first portion having an annular groove in a radial face thereof remote from said armature windings assembily increasing the creep length between said commutator and said shaft, and one of said first and second portions having an annular recess receiving and engaging an end portion of the other of said first and second sleeve portions.

3. A device as defined in claim 1 wherein said first and second sleeve portions are separable and said first sleeve portion has an axial recess receiving one end of said second portion.

4. A device as defined in claim 1 which includes an insulating spacer on said shaft adjacent said one radial face of said first sleeve portion, said groove having a minimum radial dimension at least equal to but not less than the radius of the end of said spacer adjacent thereto.

5. A device as defined in claim 4 wherein said spacer has a radially outwardly extending flange spaced axially from said sleeve means first portion, a frame supporting said armature shaft, and resilient means between said frame and said spacer and engaging the latter to resiliently, axially support said shaft relative to said frame.

6. A device as defined in claim 5 which includes bearing means carried by said frame and rotatably supporting said shaft, fiber washer means between said bearing means and said resilient means, said resilient means comprising a substantially dish-shaped spring washer embracing said fiber washer and having a radial dimension larger than said fiber washer.

7. A device as defined in claim 1 wherein said first sleeve portion has a bushing received therein and pressed on said armature shaft.

8. A device as defined in claim 6 wherein said fiber washer, said spring washer and said spacer are loosely disposed on said armature shaft.

9. A device as defined in claim 1 wherein said sleeve means second portion is molded on said armature shaft.

10. A device as defined in claim 1 which includes an armature windings assembly rotatable with said armature shaft, said sleeve means second portion being molded directly within said windings assembly and upon said armature shaft and secured thereto for rotation therewith.

11. A construction as defined in claim 2 wherein said first sleeve portion has an annular conical tapered surface between said groove and said shaft. 1

12. A construction as defined in claim 2 wherein said first sleeve portion is constructed of molded insulating material and has a bushing mounted therein adapted to be pressed on said shaft.

13. A construction as defined in claim 2 which includes frame means for rotatably supporting said shaft, resilient means loosely mounted on said shaft between said frame means and said first sleeve portion, and insulating spacer sleeve means loosely mounted on said shaft between and engaging said resilient means and said first sleeve portion and having a radial dimension not greater than the smallest radial dimension of said groove.

14. A construction as defined in claim 13 wherein said spacer sleeve means has a radial flange spaced from said first sleeve portion.

15. A construction as defined in claim 12 wherein said plastic material extends to said shaft around said bushing at the end thereof remote from said armature windings assembly.

16. A construction as defined in claim 12 wherein said plastic material extends to said bushing at the end thereof adjacent said armature windings assembly and is spaced from said shaft to define said recess, said second sleeve portion having an end portion extending within said recess adjacent said bushing.

17. A construction as defined in claim 13 wherein said resilient means includes a spring washer, bearing means carried by said frame and rotatably supporting said shaft, and a fiber washer between said bearing means and said washer and embraced by and having a radial dimension less than said washer.

18. A device a defined in claim 1 wherein said first portion has a tapered conical surface in said outer radial face radialtly inwardly of said groove.

References Cited UNITED STATES PATENTS 2,831, 991 4/1958 Perkins 310235 3,023,332 2/1962 St. Charles 310-42 3,388,459 6/1968 Dochterman 31042 WARREN E. RAY, Primary Examiner. R. SKUDY, Assistant Examiner.

US. Cl. X.R. 310-236 

